Field of the Invention
The present invention relates to a process cartridge and an image-forming method.
Description of the Related Art
The following method has been known as a general electrophotographic process that is an image-forming method. An electric latent image is formed on an electrophotographic photosensitive member (hereinafter sometimes simply referred to as “photosensitive member”), a toner is supplied to the latent image to visualize the latent image, and the toner image is transferred onto a transfer material, such as paper, followed by the fixation of the toner image onto the transfer material with heat or a pressure to provide a copy.
After the transferring step, cleaning for removing the toner remaining on the electrophotographic photosensitive member (transfer residual toner) is performed. A means that has been most widely used as a cleaning method is blade cleaning. The blade cleaning is a method involving pressing a blade-shaped member having elasticity, such as a rubber, against the surface of the electrophotographic photosensitive member to scrape off the toner.
In the blade cleaning, the toner to be removed from the surface of the photosensitive member contains not only a toner particle but also an external additive that has migrated from the toner particle to the surface of the photosensitive member. In many cases, the external additive that has migrated to the surface of the photosensitive member is more difficult to clean out than the toner particle is. One possible cause for the foregoing is as described below. The particle diameter of the external additive is smaller than the particle diameter of the toner particle, and hence the external additive enters deeper into an contacting nip between the blade and the photosensitive member, thereby increasing the probability that the external additive slips through the blade.
When the external additive that has migrated to the surface of the photosensitive member is not sufficiently cleaned out (a cleaning property is low), charging member contamination in which the external additive adheres to a charging member is liable to occur. In a region where the charging member has been contaminated, a charging process for the photosensitive member is not normally performed and hence image quality is liable to reduce. Accordingly, a mechanism for removing the external additive that has adhered to the charging member needs to be arranged, and the necessity complicates the entire mechanism, or is responsible for an increase in size of a process cartridge or in cost.
In particular, at the initial stage of the use of a brand-new process cartridge or electrophotographic apparatus, the external additive that has migrated to the surface of the photosensitive member cannot be sufficiently cleaned out in some cases. One possible cause for the foregoing is as described below. At the initial stage of the use of the brand-new process cartridge or electrophotographic apparatus, the amount of an inclusion, such as the toner, present in the contacting nip portion between the blade and the photosensitive member is small, and hence a state in which the stick-slip motion of the blade is liable to be instable is established.
In order to stabilize the stick-slip motion of the blade from the initial stage of the use of the brand-new process cartridge or electrophotographic apparatus, an attempt has been made to apply a particle of the toner, carbon fluoride, silica, or the like as a lubricant to the edge portion of the cleaning blade at the time of the production of the process cartridge or the electrophotographic apparatus. However, a measure based on the application of the lubricant to the blade leads to the complication of a production process, and hence a means of suppressing the occurrence of a cleaning failure without applying the lubricant has been required.
As a means of improving the property by which the external additive that has migrated to the surface of the photosensitive member is cleaned out, for example, an attempt has been made to increase the linear pressure at which the edge portion of the blade is pressed against the surface of the photosensitive member to prevent the slip-through of the external additive. However, a means based on the mere increase in linear pressure may cause problems such as the acceleration of the chipping of the blade edge portion, the occurrence of an abnormal noise due to the chattering vibration of the blade, and the acceleration of the abrasion of the photosensitive member.
Japanese Patent Application Laid-Open No. 2007-279702 proposes an approach to improving the cleaning property through the use of a large-particle diameter silica particle that is nonspherical and amorphous as the external additive. However, the use of a large-particle diameter inorganic external additive may impair the low-temperature fixability of the toner. Accordingly, there is a possibility that the power consumption in a fixing step may increase.
Japanese Patent Application Laid-Open No. 2002-318467 proposes an approach to improving the cleaning property through the formation of a layer, in which a large-particle diameter amorphous or abrasive particle is retained, on the blade edge portion. However, with the approach proposed in Japanese Patent Application Laid-Open No. 2002-318467, it is difficult to suppress the slip-through of a small-particle diameter external additive, though a toner particle larger than the large-particle diameter amorphous or abrasive particle can be cleaned out. In addition, in order to form a stable retention layer on the blade edge portion, the large-particle diameter amorphous or abrasive particle needs to be sufficiently supplied to the blade edge portion by activating an electrophotographic process to some extent. Accordingly, it is assumed that in the first place, an improving effect on the cleaning property by the formation of the retention layer is not sufficiently obtained at the initial stage of the use of the brand-new process cartridge or electrophotographic apparatus.